The present invention relates to document processing equipment, and more particularly to adjusting document nudger drive friction force in a document feeding device.
Document feeding devices are commonly used today to quickly move and sort a variety of documents. Documents are often stacked and automatically fed from the document stack. A feeding mechanism, typically including a nudger and a feedwheel/separator nip, is used to introduce each document to its document transport for processing and sorting. It is important to introduce each document singly, with consistent spacing to permit the fastest feed rate possible while still maintaining proper document spacing.
In high-speed equipment, a hopper is often used to supply documents toward the nudger. A stack of documents is placed in the hopper against a flag element, which is used to move the document stack toward the nudger during feeding. To move the document stack, the flag applies a force to the last document in the stack, thereby forcing the stack against a nudger belt.
It is common to apply the flag force with a spring, a weight, or a motor. Most commonly, an electric motor drives a cable drum which is interconnected to the flag element by a flexible cable. By applying an electric current to the motor, a known torque is applied to the drum. Rotation of the drum produces a tension on the flexible cable, and subsequently, a force on the flag element.
As the flag force moves the document stack along the hopper, the stack is supported by a hopper floor and is guided along a leading edge guide wall toward the nudger. Upon reaching the nudger, the nudger belt (driven by a nudger belt pulley) drives the documents from the stack toward the feedwheel/separator nip. At the feedwheel/separator nip, documents are separated to other transports for forwarding to upstream document processing stations and/or to sorters.
As is often the case in conventional systems, the nudger may inadvertently drive more than one document from the stack or may apply a force to a document when the trailing edge of a previous document has not yet left the feedwheel/separator nip. In such a circumstance, depending on inter-document friction and fragility of the document, document leading edge damage, overlapped document feeding, or document jamming may occur if the nudger drive friction force is too large. In contrast, if the nudger drive friction force is too small, a document may slip on the nudger belt and not be driven to the feedwheel/separator nip.
Furthermore, although the electric motor torque may be reliable and consistent, the normal force at the nudger due to the motor may vary due to losses between the motor and the nudger. These losses may be induced by cable bending, cable idler friction, flag guide friction, and/or variable friction between the differing documents and the hopper floor and leading edge guide. Also, the coefficient of friction between the nudger belt and the documents may vary depending upon the documents and the environmental conditions, and the age of the nudger belt material.
It is therefore desirable to adjust the nudger force in response to force changes caused by such variables in order to provide consistent document spacing.
Accordingly, the present invention is provided to alleviate some of the shortcomings of conventional systems. In a preferred embodiment of the present invention, a nudger drive friction force is measured and compared with a desired nudger belt friction force term needed for reliable feeding. Cable drum motor torque is responsively adjusted to obtain a desired nudger drive friction force.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.